Add string interpolation to FilteringBoundLogger

.github/workflows/ci.yml

@@ -107,6 +107,7 @@ jobs:
       fail-fast: false
       matrix:
         python-version:
+          # mypy on 3.7 fails but there's nothing we can do about it
           - "3.8"
           - "3.9"
           - "3.10"
@@ -128,6 +129,7 @@ jobs:
       - uses: actions/checkout@v3
       - uses: actions/setup-python@v4
         with:
+          # Keep in sync with tox.ini/docs & readthedocs.yml
           python-version: "3.10"
       - run: python -m pip install --upgrade wheel tox
 

CHANGELOG.md

@@ -25,6 +25,18 @@ So please make sure to **always** properly configure your applications.
   Please use [`importlib.metadata`](https://docs.python.org/3.10/library/importlib.metadata.html) instead (for Python 3.7: the [*importlib-metadata*](https://pypi.org/project/importlib-metadata/) PyPI package).
 
 
+### Added
+
+- `FilteringBoundLogger` (used by default) now allows for string interpolation using positional arguments:
+
+  ```pycon
+  >>> log.info("Hello %s! The answer is %d.", "World", 42, x=1)
+  2022-10-07 10:04.31 [info     ] Hello World! The answer is 42. x=1
+  ```
+
+  [#454](https://github.com/hynek/structlog/pull/454)
+
+
 ### Changed
 
 - The build backend has been switched to [*Hatch*](https://hatch.pypa.io/).

readthedocs.yml

@@ -5,7 +5,7 @@ formats: all
 build:
   os: ubuntu-20.04
   tools:
-    # Keep version in sync with tox.ini (docs and gh-actions).
+    # Keep version in sync with tox.ini/docs and ci.yml/docs
     python: "3.10"
 
 python:

src/structlog/_log_levels.py

@@ -126,8 +126,8 @@ def make_method(level: int) -> Callable[..., Any]:
 
         name = _LEVEL_TO_NAME[level]
 
-        def meth(self: Any, event: str, **kw: Any) -> Any:
-            return self._proxy_to_logger(name, event, **kw)
+        def meth(self: Any, event: str, *args: Any, **kw: Any) -> Any:
+            return self._proxy_to_logger(name, event % args, **kw)
 
         meth.__name__ = name
 

src/structlog/types.py

@@ -151,6 +151,8 @@ class FilteringBoundLogger(BindableLogger, Protocol):
     The only way to instantiate one is using `make_filtering_bound_logger`.
 
     .. versionadded:: 20.2.0
+    .. versionadded:: 22.2.0
+       String interpolation using positional arguments.
     """
 
     def bind(self, **new_values: Any) -> FilteringBoundLogger:
@@ -181,53 +183,53 @@ def new(self, **new_values: Any) -> FilteringBoundLogger:
         .. versionadded:: 22.1.0
         """
 
-    def debug(self, event: str, **kw: Any) -> Any:
+    def debug(self, event: str, *args: Any, **kw: Any) -> Any:
         """
-        Log *event* with **kw** at **debug** level.
+        Log ``event % args`` with **kw** at **debug** level.
         """
 
-    def info(self, event: str, **kw: Any) -> Any:
+    def info(self, event: str, *args: Any, **kw: Any) -> Any:
         """
-        Log *event* with **kw** at **info** level.
+        Log ``event % args`` with **kw** at **info** level.
         """
 
-    def warning(self, event: str, **kw: Any) -> Any:
+    def warning(self, event: str, *args: Any, **kw: Any) -> Any:
         """
-        Log *event* with **kw** at **warn** level.
+        Log ``event % args`` with **kw** at **warn** level.
         """
 
-    def warn(self, event: str, **kw: Any) -> Any:
+    def warn(self, event: str, *args: Any, **kw: Any) -> Any:
         """
-        Log *event* with **kw** at **warn** level.
+        Log ``event % args`` with **kw** at **warn** level.
         """
 
-    def error(self, event: str, **kw: Any) -> Any:
+    def error(self, event: str, *args: Any, **kw: Any) -> Any:
         """
-        Log *event* with **kw** at **error** level.
+        Log ``event % args`` with **kw** at **error** level.
         """
 
-    def err(self, event: str, **kw: Any) -> Any:
+    def err(self, event: str, *args: Any, **kw: Any) -> Any:
         """
-        Log *event* with **kw** at **error** level.
+        Log ``event % args`` with **kw** at **error** level.
         """
 
-    def fatal(self, event: str, **kw: Any) -> Any:
+    def fatal(self, event: str, *args: Any, **kw: Any) -> Any:
         """
-        Log *event* with **kw** at **critical** level.
+        Log ``event % args`` with **kw** at **critical** level.
         """
 
-    def exception(self, event: str, **kw: Any) -> Any:
+    def exception(self, event: str, *args: Any, **kw: Any) -> Any:
         """
-        Log *event* with **kw** at **error** level and ensure that ``exc_info``
-        is set in the event dictionary.
+        Log ``event % args`` with **kw** at **error** level and ensure that
+        ``exc_info`` is set in the event dictionary.
         """
 
-    def critical(self, event: str, **kw: Any) -> Any:
+    def critical(self, event: str, *args: Any, **kw: Any) -> Any:
         """
-        Log *event* with **kw** at **critical** level.
+        Log ``event % args`` with **kw** at **critical** level.
         """
 
-    def msg(self, event: str, **kw: Any) -> Any:
+    def msg(self, event: str, *args: Any, **kw: Any) -> Any:
         """
-        Log *event* with **kw** at **info** level.
+        Log ``event % args`` with **kw** at **info** level.
         """

tests/test_log_levels.py

@@ -103,3 +103,11 @@ def test_pickle(self, level):
         bl = make_filtering_bound_logger(level)
 
         assert bl == pickle.loads(pickle.dumps(bl))
+
+    def test_pos_args(self, bl, cl):
+        """
+        Positional arguments are used for string interpolation.
+        """
+        bl.info("hello %s -- %d!", "world", 42)
+
+        assert [("info", (), {"event": "hello world -- 42!"})] == cl.calls

tox.ini

@@ -5,7 +5,7 @@ ignore = E203,W503,W504
 # We don't run pre-commit in CI, because we use pre-commit.ci.
 [gh-actions]
 python =
-    3.7: py37  # mypy on 3.7 fails but there's nothing we can do about it
+    3.7: py37
     3.8: py38
     3.9: py39
     3.10: py310

typing_examples.py

@@ -310,3 +310,6 @@ def typecheck_filtering_return() -> None:
         structlog.processors.JSONRenderer(),
     ]
 )
+
+fbl: FilteringBoundLogger = structlog.get_logger()
+fbl.info("Hello %s! The answer is %d.", "World", 42, x=1)